Nonionic cellulose ethers are generally known in the art. They are employed in a variety of industrial applications, as thickeners, as water retention aids, and as suspension aids in certain polymerization processes, among others.
U.S. Pat. No. 4,462,837 discloses a cement with a hydroxyethylcellulose ether (HECE) having a critical viscosity or a mixture of HECE and hydroxypropylcellulose ether of a critical viscosity plus a dispersant.
EP 0314188 discloses the use of hydrophobically modified cellulose ethers, such as hydrophobically-modified hydroxyethyl cellulose having a hydroxyethyl molar substitution (MS) of 1.5 and a long chain alkyl group modifier having 6 to 25 carbon atoms.
U.S. Pat. No. 4,784,693 discloses the use of hydrophobically-modified hydroxyethyl cellulose (HMHEC) having 0.2 to 4 weight percent hydrophobic substitution, an MS (hydroxyethyl) substitution of 1.5 to 4 and a viscosity of 300 to 500 cps, measured as a 1 weight percent aqueous solution, for use as a fluid-loss additive in oil-well cementing.
U.S. Pat. No. 4,529,523 discloses the use of hydrophobically modified cellulose ethers, such as hydrophobically-modified hydroxyethyl cellulose having about 1 weight percent hydrophobic substitution, an MS (hydroxyethyl) substitution of 2.5 and molecular weights of 50,000 to 1,000,000, preferably about 150,000 to 800,000, as water flooding medium for the recovery of petroleum.
U.S. Pat. No. 4,228,277 discloses nonionic methyl, hydroxyethyl or hydroxypropyl cellulose ethers substituted with long chain alkyl radicals having 10 to 24 carbon atoms in an amount between about 0.2 weight percent and the amount which renders the cellulose ethers less than 1 percent by weight soluble in water. The products exhibit improved viscosifying behavior compared to their unmodified cellulose ether counterparts.
US 2008/0300151 (A1) describes the use of aqueous fluidized polymer suspensions comprising an allyloxy based copolymer for use in oilfield applications, including cementing.
US 2005/027905 (A1) describes the use of hydrophobically-modified polyamines or polyacrylates as fluid loss control additives in cementing applications.
However, many of these known water-soluble or water-swellable cellulose ethers used as rheology modifiers or thickening agents exhibit a reversible loss of viscosity at elevated temperatures, referred to as thermal thinning. In many end-use applications, such as water, petroleum and natural gas recovery (e.g., cementing wells, hydraulic fracturing, and enhanced oil recovery), geothermal wells (fracturing and cementing), construction (e.g., concrete pumping and casting, self-leveling cement, extruded concrete panels), full-depth road reclamation, ceramics (e.g., as green strength additive), metal working and cutting fluids, thermal thinning is highly undesirable.
There has been some progress in designing water-soluble cellulose ethers used as rheology modifiers or thickening agents which demonstrate reduced thermal thinning. However, these improvements typically result in higher viscosities at lower (ambient) temperatures which adversely affect the pumpability of the said compositions under normal conditions of cementing casings in boreholes. These unsuitably high viscosities can prevent the addition of some polymeric additives in sufficient levels to perform the desired function. That is, a polymer that may impart desirable properties on a cement formulation, such as fluid loss control, may go unused due to the undesirable effect of generating very high cement slurry viscosity, preventing pumping of said slurry. This viscosity limitation is especially vexing for high molecular weight polymers, and even more challenging for hydrophobically-modified high molecular weight polymers which might otherwise be quite viable cement additives.
An additional limitation of hydrophobically-modified polymers is that these highly-engineered polymers are often expensive to produce, due to the required additional reactive step of incorporating the hydrophobe. As such, use of such polymers at the same loading level as other polymers can make them economically disadvantaged. It is thus further desirable to design additive combinations that impart desirable properties while using low levels of the hydrophobically-modified polymer additive.
Accordingly, it would be desirable to find a new cellulose ether composition which exhibits reduced fluid loss and thermal thinning, especially at high temperatures e.g., above 190° F., while maintaining an adequately low viscosity at ambient (i.e., pumping) temperatures. It would be further desirable to find additive combinations that allow the use of high molecular weight hydrophobically-modified polymers without generating prohibitively high viscosities. Finally, additive combinations that require only low levels of hydrophobe-modified polymer additive are especially desirable.